The present disclosure generally relates to a downhole tool employed during hydrocarbon exploration activities. Specifically, the present disclosure relates to devices and methods for measuring inclination or deviation from a vertical axis of a downhole tool.
In the drilling wells for production of hydrocarbons, it is often necessary to determine the inclination of a downhole tool or a portion of a drill string. Knowledge of the inclination, otherwise known as deviation from the vertical, is often desirable to determine the direction a sub-surface end of a drill string is oriented so that adjustments may be made to properly orient the drill string while drilling a borehole. Further, measurement of the inclination of the drill string may provide an indication of the borehole inclination at the point the measurement is made. In many instances, laws or other regulations require measurement of a borehole inclination at specified interval distances, typically every 1,000 ft. Further, it is often undesirable for boreholes to intersect other boreholes, such as multiple boreholes from a single platform. Determination of inclination may assist in avoiding such intersection.
Conventional mechanical methods in the art for measuring drill string inclination usually involve a complicated swinging pendulum mechanism. Essentially, in the conventional mechanical prior art systems, a pendulum device swings outwardly in response to an inclination or a deviation from a vertical axis. The pendulum device moves axially through a number of increasingly restrictive rings until the pendulum “hooks” or catches one of the restrictive rings preventing further axial movement of the pendulum. These conventional mechanical methods typically involve coding systems that translate small movements of a pendulum and rod into relatively long movements of a pressure pulse knob for communicating inclination measurement information to the surface via a series of pressure wave pulses through the drilling mud.
Unfortunately, these conventional mechanical devices for measuring inclination suffer from a number of significant disadvantages. In particular, the pendulum mechanisms are complicated and comprise many moving parts. Consequently, these conventional mechanical systems are expensive and prone to failure, particularly in the hostile conditions normally encountered in downhole environments. Additionally, because relatively small movements of the pendulum mechanisms are typically used to signal inclination measurements, the pendulum mechanisms sometimes suffer from unacceptably poor accuracy. In some instances, the pendulum mechanisms have been known to fail to properly engage at the desired inclination due to vibration or due to excessive axial speed of the pendulum device during inclination measurement. Consequently, these devices are known to be sometimes unreliable.
Accordingly, mechanical devices for measuring inclination and methods are needed to address one or more of the disadvantages of the prior art.